Internal combustion engines are used as the primary power plant for modern day vehicles. The engines rely upon the expansion of gases within cylinder heads wherein pistons, connecting rods, and a crank shaft convert a controlled explosion in a cylinder chamber into rotational movement. Control of the cylinder chamber is performed by sequential operation of intake and exhaust valves operated in conjunction with an overhead valve design incorporating a camshaft, cam follower, push rod, and rocker arm for conducting air flow into and out of the cylinder chambers. The stress on these components is dramatically increased in those instances where the valve train must perform at higher than normal engine speeds such as those associated with high performance vehicles.
Specialty rocker arms and valve train assemblies capable of withstanding high stress are typically modified from mass produced internal combustion engines. Over the years many aberrations were developed around original equipment manufactured by the Ford Motor Company, General Motors, and the Chrysler Corporation. As these valve train components evolved, two factions of product groups within the after market industry also evolved as separate entities which focus mainly on their independent forte in developing of components related to the valve train. Both depend upon each other for compatibility in providing optimum performance. The valves are contained within the cylinder head, the rocker arm portion is mounted upon the cylinder head and operatively associated with the valves. The rocker arm and the valve train design criteria is influenced by the parameters established in the cylinder head design: often appearing as though each manufacturing entity is unaware or oblivious to the others' needs.
Rocker arms transfer the operational timing of a precision designed and manufactured component, the camshaft, and further increase the cam's instructions of movement by means of a mechanical increase in ratio, usually between 1.5:1 and 2.0:1, requiring utmost precision in operation to obtain maximum efficiency. The problem is that rocker arms inherently suffer from wear and fatigue imposed through the variables of heat and flex: a foremost element of operation which amplifies and accelerates these consequences. While in-line valves and in-line rocker arm shafts are traditional designs within the industry, staggered valves or valves sitting at compound angles have forced the current art of this technology to adapt independent rocker arm designs. These designs provide for a compound angle rocker arm mounting which has been addressed as only a single rocker arm mounted upon a single shaft placed at the appropriate compound angle to maintain an even contact with the valve stem lip throughout the valve's travel, sacrificing the rigidity. Many cylinder heads now employ compound angle valves placing the associated rocker arms at compound angles to facilitate proper alignment with the valve's centerline during valve lifter operation.
Roller tip rocker arms for automobile applications, initially made of aluminum, are traceable to the late 1950's, with a series of different companies over the years giving birth to a variety of different designs, materials and applications; none of which has established a science of design which is precedent setting to all applications; although it was from this arena that the current "technology" of rocker arms arose. Today, these components are deemed an asset in relieving or minimizing friction with the engine's valve train for all types of vehicle applications. When rocker arms use a roller that is radiated on its outside diameter to provide a pivoting axis that is not in alignment with the valve's centerline of motion, or on cylinder heads which, for whatever reason, have in-line rocker arm shafts that allow the rocker arm to pivot parallel to the camshaft and perpendicular to the valve's linear travel, this can provide increased rigidity and a more simple stand design to further that rigidity.
Thus, a primary problem with the prior art rocker arm stand is directed to the various heights and angles used to accommodate placement of the intake and exhaust valves in conjunction with the push rods operated by a camshaft. While the offset geometry allowed for more fluent operation of the valves and push rods, the rocker arm stands have to be placed at different elevations and angled to accommodate the valve and push rod. For this reason, a situation occurs in maintaining rigidity to the rocker arm movement which can alter performance of the vehicle and is most notable in high performance engines.
One method used by high performance fabricators for lessening the movement of the rocker arm components is by welding the rocker arm stands together. Despite the benefit of increased rigidity, welding is permanent, lessening the ability for rocker arm change-out. In addition, welding tempers the steels which may lead to a faulty component during a high stress situation.
Another method of increasing the rigidity of rocker arm stands is the use of a rod like structure which bolts a plurality of studs together, commonly known as a stud girdle. The stud girdle simply couples the upper portion of mounting studs and does not address the cause for lack of rigidity. Further, stud girdles are complicated structures when used in combination with compound geometry cylinder heads.
Thus, what is lacking in the art is a method and apparatus for eliminating the compound angles used in accommodating the angular valve placement to provide the benefits of offset valve arrangement with an ability to stabilize rocker arm placement thereby.